As recording densities in hard disk drives (HDD) increase, fly height of a read/write head must decrease to properly read/write data on the disk. Accordingly, the disk surface must be very smooth and free of asperities that may deleteriously affect the HDD. Therefore, there must be sensors that can detect the disk asperities.
Typically, asperities are detected when a glide head physically contacts the asperities. As the asperities hit the glide head, the glide head vibrates in a characteristic mode (e.g., first bending, second bending, torsion, etc.). The vibrations are detected by a PZT sensor on the glide head, which in turn, produces an electrical signal. However, due to decreasing size of asperities, the amplitude of vibration is becoming too small to be detected by a PZT sensor and/or may not even be detected.
The drawings referred to in this description should be understood as not being drawn to scale except if specifically noted.